From 3fe7fa5843d204e235d92902190fecb972a3f9cc Mon Sep 17 00:00:00 2001
From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Date: Fri, 10 Dec 2021 15:09:21 -0500
Subject: [PATCH] mm: Add folio_put_refs()
This is like folio_put(), but puts N references at once instead of
just one. It's like put_page_refs(), but does one atomic operation
instead of two, and is available to more than just gup.c.
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
---
include/linux/mm.h | 20 ++++++++++++++++++++
1 file changed, 20 insertions(+)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index c768a7c81b0b1..cb98f75b245e8 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1244,6 +1244,26 @@ static inline void folio_put(struct folio *folio)
__put_page(&folio->page);
}
+/**
+ * folio_put_refs - Reduce the reference count on a folio.
+ * @folio: The folio.
+ * @refs: The amount to subtract from the folio's reference count.
+ *
+ * If the folio's reference count reaches zero, the memory will be
+ * released back to the page allocator and may be used by another
+ * allocation immediately. Do not access the memory or the struct folio
+ * after calling folio_put_refs() unless you can be sure that these weren't
+ * the last references.
+ *
+ * Context: May be called in process or interrupt context, but not in NMI
+ * context. May be called while holding a spinlock.
+ */
+static inline void folio_put_refs(struct folio *folio, int refs)
+{
+ if (folio_ref_sub_and_test(folio, refs))
+ __put_page(&folio->page);
+}
+
static inline void put_page(struct page *page)
{
struct folio *folio = page_folio(page);
--
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